Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
1998-07-13
2001-02-20
Shalwala, Bipin (Department: 2778)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S087000, C345S098000, C345S111000, C345S210000, C341S144000
Reexamination Certificate
active
06191779
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active-matrix type liquid crystal display device having a switching element for each pixel, and more particularly to a dot-inversion type liquid crystal display device which supplies voltages of different levels to the two switching elements corresponding to adjacent pixels.
2. Discussion of the Background
Thin Film Transistor (TFT) type liquid crystal display devices comprise a switching element and a pixel electrode (display electrode) for each of their pixels. Such devices are constituted in order that a transmittance of a liquid crystal layer changes depending on a voltage applied to the pixel electrode. One end of the switching element is supplied with a voltage in accordance with pixel data, and a voltage of the pixel electrode is controlled in accordance with the voltage applied to the switching element.
Unchanged application of a voltage in the same direction to the liquid crystal layer gives rise to fixing of an arrangement of the liquid crystal, resulting in a slow motion of the liquid crystal and blackish displaying. Therefore, in order to cope with such problem, a liquid crystal display device adopting an inversion driving type, which allows the voltage applied to the liquid crystal layer to make an inversion in one frame unit (one screen), in one horizontal line unit or in one pixel unit, has been proposed. As shown in FIG.
1
and described below, a positive side analog voltage is applied to a first pixel of the liquid crystal layer and a negative side analog voltage is applied to an adjacent pixel. Because separate voltages are generated, the associated circuit may introduce time delays between these signals. Also such a circuit may process pixel data having a large number of bits. Thus the circuit may have a large power consumption for processing such data.
For portable equipment driven with a battery, such as notebook type computers and electrical pocketbooks, lengths of driving time of the battery are essential factors which determine the added values of products, and products with a battery having a short life because of a large power consumption have a low commercial value, resulting in a lack of the competitive power in many cases.
SUMMARY OF THE INVENTION
From the foregoing, an object of the present invention is to provide a liquid crystal display device which consumes less power and causes no signal delay when a liquid crystal panel performs an inversion-type drive.
In order to achieve the foregoing object, the first aspect of a device for controlling a liquid crystal display device of the present invention comprises a digital control circuit which receives a first voltage and a second voltage higher than the first voltage as reference voltages and outputs a plurality of digital pixel data, a plurality of capacitors, a charging control circuit and a digital-to-analog (D/A) converter. Each capacitor has a first terminal coupled to the digital control circuit to receive a corresponding one of the plurality of digital pixel data. Each input terminal of the charging control circuit is coupled to a second terminal of a corresponding one of the capacitors. The D/A converter is coupled to each output terminal of the charging control circuit, and receives a fourth voltage and a fifth voltage higher than the fourth voltage as reference voltages, and outputs an analog voltage signal to a liquid crystal panel. After data is outputted from the charging control circuit, each second terminal of the capacitors is charged to a third voltage, charging is stopped in order to set each of the second terminals of the capacitors to a floating state, and the digital pixel data are outputted from the digital control circuit.
The second aspect of a semiconductor device for controlling a liquid crystal display device of the present invention comprises a digital control circuit which receives a first voltage and a second voltage higher than the first voltage as reference voltages and outputs first and second digital pixel data, a plurality of capacitor elements, a charging control circuit, first and second D/A converters, and a switch. Each capacitor has a first terminal coupled to receive the first digital pixel data. Each input terminal of the charging control circuit is coupled to a second terminal of a corresponding one of the capacitors. The first D/A converter is coupled to each output terminal of the charging control circuit, and receives a fourth voltage and a fifth voltage higher than the fourth voltage as reference voltages, and outputs a first analog voltage signal. The second D/A converter receives the second digital pixel data outputted from the digital control circuit and receives a sixth voltage signal and a seventh voltage higher than the sixth voltage, and outputs a second analog voltage signal. The first switch alternately switches in order to selectively apply either the first or second analog voltage signals to a liquid crystal panel at a predetermined timing. After data is outputted from the charging control circuit, each second terminal of the capacitors is charged to a third voltage, charging is stopped in order to set each second terminal of the capacitors to a floating state, and the first digital pixel data is outputted from the digital control circuit.
In one of the first and second aspects of the semiconductor device for controlling a liquid crystal display device of the present invention, the third aspect of the present invention has a feature in that after either the first digital pixel data or the second digital pixel data is outputted, either data obtained by adding the second voltage to the third voltage or data obtained by adding the first voltage to the third voltage is outputted from the charging control circuit via the capacitors.
In one of the first to third aspects of the semiconductor device for controlling a drive of a liquid crystal display device, the fourth aspect of the present invention has a feature in that the capacitors are charged during a blanking period from the completion of a displaying period of one horizontal line until the beginning of a displaying period of the next horizontal line.
In one of the first to fourth aspects of the semiconductor device for controlling a liquid crystal display device, the fifth aspect of the present invention has a feature in that the charging control circuit comprises a second switch having one terminal coupled to the capacitors and the other terminal coupled to the third voltage.
In one of the first to fifth aspects of the semiconductor device for controlling a liquid crystal display device, the sixth aspect of the present invention has a feature in that the charging control circuit comprises a diode having a cathode terminal coupled to the capacitors and an anode terminal set to the third voltage.
In the fifth aspect of the semiconductor device for controlling a liquid crystal display device, the seventh aspect of the present invention has a feature in that the second switch is turned on or off by a switching signal outputted from the digital control circuit.
In one of the first to seventh aspects of the semiconductor device for controlling a liquid crystal display device, the eighth aspect of the present invention has a feature in that a potential difference between the first and second voltages is set to be equal to the voltage difference between the fourth and fifth voltages.
In one of the first to eighth aspects of the semiconductor device for controlling a liquid crystal display device, the ninth aspect of the present invention has a feature in that a potential difference between the fourth and fifth voltages is set to be equal to the voltage difference between the sixth and seventh voltages.
In one of the first to ninth aspects of the semiconductor device for controlling a liquid crystal display device, the tenth aspect of the present invention has a feature in that the third voltage is equal to the fourth voltage.
In one of the first to tenth aspects of the semiconductor device for controlling a l
Itakura Tetsuro
Taguchi Takashi
Kabushiki Kaisha Toshiba
Kovalick Vincent E.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Shalwala Bipin
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